Question

Q1. 20cm³ of a gaseous hydrocarbon and 150cm³ of oxygen were exploded in a closed vessel. After cooling, 110cm³ of gases remained. After absorption by concentrated NaOH solution, the volume left was 50cm³. Determine the molecular formula of the hydrocarbon

Answer 1

1. 110 cm³ - 50 cm³ = 60 cm³ it`s CO₂
2. 50 cm³ - unburnt oxygen
3. 150 cm³ - 50 cm³ = 100 cm³ consumed oxygen

$$20C_xH_y + 100 O_2 = 60 CO_2 + zH_2O$$

5.

$$2C_xH_y + 10O_2 = 6CO_2 + 8H_2O$$

6.

$$C_xH_y + 5O_2 = 3CO_2 + 4H_2O$$

7.

$$x = 3; y = 8.$$

Answer: C₃H₈